Apparatus and methods for performing work on vessel hulls in a drydock have been known in the past. For example, U.S. Pat. Nos. 5,211,125; 5,353,729; 5,355,823; and 5,398,632, which are incorporated herein for all purposes, propose apparatus and methods for performing external surface work on ship hulls.
Vessels, which include ships, boats and barges, are positioned on a drydock for building and repairing. Generally, a drydock is a large floating vessel used by shipyards to lift barges, boats, and ships so that repair work may be performed on them out of the water. Drydocks often have many structural steel beams which run across the deck or top surface to add strength as well as multiple blocks, which are often fabricated from wood, on which the vessels rest. Most drydocks include wing walls on each side of the drydock. These wing walls contain buoyancy tanks which are filled with water to submerge the drydock.
It has also been known in the past that when a vessel overhangs beyond the end of a drydock, floating, but not submersible, floats or barges can be placed beneath the overhanging portion of the vessel to catch pollutants, such as, spent abrasives from sandblasting, paint chips, rust and dust.
One known method for controlling pollutants, such as spent abrasives, accumulated in sandblasting operations on a vessel is to allow the pollutants to fall through a grating which replaces the deck or top surface on which the workers stand. The pollutants fall through the grating land in a chamber, where the pollutants are later moved to shore by means of pumping.
The Environmental Protection Agency ("EPA") has promulgated regulations related to the "Best Management Practices" ("BMP") for ship and boat building and repairing yards in volume 60, number 189 of the Sep. 29, 1995 Federal Register. The EPA has identified the common pollutant sources at ship and boat building and repairing facilities. For example, activities such as surface preparation, paint removal and sanding involve sanding, mechanical grinding and abrasive blasting with resulting pollutants of spent abrasives, paint chips, rust and dust. Also, the activity of painting involves paint and paint thinner, spray painting, sanding and paint cleanup with resulting pollutants of paint chips, rust and dust.
To control these resulting pollutants from these drydock activities, the EPA Best Management Practices provide for storm water pollution prevention relating to certain activities at ship and boat building and repairing facilities including 1.) surface preparation, sanding and paint removal, 2.) painting, 3.) drydock maintenance, and 4.) drydock activities. One such practice that the EPA suggests for surface preparation, sanding, paint removal and drydock maintenance is sweeping the drydock before each submersion to minimize potential for pollutants. However, sweeping large drydocks is highly labor intensive and consumes significant dock time, making the process excessively expensive.
In order to comply with Sec. 101 of the Federal Water Pollution Control Act, as amended by the Clean Water Act of 1977 (FWPC), shipyards should not discharge water, which comes into contact with pollutant sources, without removing the pollutants. Thus, if pollutants are not swept from a drydock before submersion, an approved control device must prevent such pollutants from entering the water during submersion.
Another BMP identified by the EPA for drydock activities is the use of plastic barriers hung from the wing walls of the drydock, from the bow or stern of the vessel, or from temporary structures for containment of abrasives, paint chips and overspray. U.S. Pat. No. 4,787,179 discloses an abrasive blasting containment land based system for cleaning large steam turbines.
Shipyards have been known in the past to use lightweight polypropylene containment to reduce emissions of sand, dust and overspray to the atmosphere. This "ARMORLON" containment material has been recommended for shipyard barge blasting by Reef Industries, Inc. of Houston, Texas. However, this containment method, as recommended by the EPA, does not address the above discussed problem of the high costs associated with sweeping of a drydock before each submersion.
Therefore, there has been and is a need, as identified by the above EPA promulgation, in the ship and boat building and repair industry for a way to cost effectively control pollutants in drydock activities, to comply with the FWPC, EPA and state authorities regulations for effluent limitations of pollutants from a drydock used in construction, repairing and cleaning of ships, barges, tugs, and boats. In particular, a process and system for reducing the labor intensive clean up of pollutants created during surface preparation, sanding, paint removal, painting and other drydock activities while properly controlling pollutants would be highly desirable.
In summary, it would be highly desirable to have a system and process that would control pollutants to a level below maximum allowable regulatory effluent limitations for water, without the labor intensive task of sweeping the entire drydock deck or top surface before the submersion of the drydock.